Revelation 20:1-3

And then I saw an angel descending from heaven, holding the key of the abyss (the bottomless pit) and a great chain was in his hand. And he overpowered and laid hold of the dragon, that old serpent [of primeval times], who is the devil and Satan, and bound him [securely] for a thousand years (a millennium); [Rev 12:7-9, 12, 15] and the angel hurled him into the abyss, and closed it and sealed it above him [preventing his escape or rescue], so that he would no longer deceive and seduce the nations, until the thousand years were at an end. After these things he must be liberated for a short time.